Owing to the recent diffusion of the Internet, various digital contents including a computer file are actively distributed on a network. Moreover, with the spread of a broadband communication network (xDSL (x Digital Subscriber Line), CATV (Cable TV), a wireless network or the like), a mechanism capable of transmitting the distribution of digital data such as music data, image data or electronic publication and even rich contents such as a motion picture without giving any stresses to a user is now being arranged.
On the other hand, the distributed contents are digital data, and therefore, an unauthorized operation such as copy or falsification can be relatively easy to perform. Moreover, a fraud such as the copy or the falsification of the contents is currently frequently committed, which is a main cause of hampering the interest of a digital-content vendor. As a result, a vicious cycle that the price of the contents must be increased to result in the hindrance of diffusion is generated.
For example, recently, the technology of a computer, a network or the like is steadily spreading to general households. An information device such as a personal computer for home use or a PDA (Personal Digital Assistants) and, in addition, various information home appliances such as a television set and a video playback device are interconnected via a home network. In many cases, such a home network is interconnected to an external broadband network including the Internet via a router. After the contents legitimately acquired from a server on the Internet are stored in a server on the home network (hereinafter, referred to as a “home server”), the contents are distributed via the home network to another in-home terminal (client).
Under the copyright law, the contents as copyright work are protected against unauthorized use such as unauthorized copy or falsification. On the other hand, an authorized user is allowed to copy the contents for private use, that is, for personal use, family use or other similar uses within a limited circle (see Copyright Law of Japan, Article 30).
If the scope of private use is applied to the above-described home network, the client terminal connected to the home network is supposed to be within the scope of personal use or family use. Therefore, it is considered that it is appropriate for the client terminal on the home network to make free use of the legitimately acquired contents in the home server (it is apparent that the number of terminals which can enjoy the contents is required to be limited to a certain number).
With a current technique, however, it is difficult to determine whether a client terminal logging into the home network is within the scope of private use or not.
For example, since the home network is interconnected to an external network via a router based on an IP protocol, the home server does not know where a client making access actually is. If the home server provides the contents to external (remote) access, the use of the contents is substantially unrestrained. Therefore, the copyright for the contents is almost unprotected. As a result, a content creator may lose the motivation of the creation.
Furthermore, if the home server allows the client terminal in the home network to use the contents in the same manner, the same client terminal logs into a plurality of home networks at time intervals. As a result, it can use the contents almost unrestrictedly.
On the other hand, if strict restrictions are imposed on the client terminal, a user cannot ensure the private use fundamentally allowed by the copyright law. As a result, the user cannot satisfactory enjoy the contents. Accordingly since the use of a home server or a content-distribution service is not well promoted, the development of content business itself may be impeded.
For example, in consideration of the fact that a user who legitimately purchases copyright work is allowed for free use of it, a method for more easily obtaining consent from an owner of the rights to the contents for the copy and the use of information on a network by the user has been proposed (see, for example, Japanese Patent Application Publication No. 2002-73861). However, this method classifies users depending on the level of relation with the owner of the rights to the use of information and distributes the information by a different distribution method for each level of the relation. This method does not identify the extent of the scope of private use on the network.
Meanwhile, as a protocol constituting the home network, for example, an UPnP (registered trademark) has been known. The UPnP allows easy network construction without any complicated operations and allows a content-providing service between network-connected devices without any difficult operations and setting. Moreover, the UPnP is advantageous in that it is not dependent on an operating system (OS) and the addition of a device is easy.
In the UPnP, network-connected devices exchange a definition file described in an XML (eXtensible Markup Language) format for mutual authentication. The outline of processing of the UPnP is as follows.    (1) Addressing process: its own device ID such as an IP address is acquired.    (2) Discovery process: each device on a network is searched so as to acquire information such as device type or a function contained in a response received from each device.    (3) Service request process: a request is made for a service to each device based on information acquired by the discovery process.
By such a processing procedure, a service can be provided and received using network-connected devices. A device to be connected to the network acquires a device ID by the addressing process and acquires information for other devices on the network by the discovery process, thereby enabling a service request.
The contents stored in the home server can be accessed from other devices on the home network. For example, the contents can be acquired by a device implementing the UPnP connection. If the contents are video data or audio data, a TV or a player is connected as a network-connected device so that a movie or music can be enjoyed.
However, in the device within the home network, for example, in the home server, the contents requiring copyright management such as private contents or pay contents are stored. Therefore, it is necessary to consider the countermeasure against unauthorized access.
It is natural that access from a device of a user having the rights to the use (a license) of the contents is allowed. However, in a home network environment interconnected to the external network via a home router, even a user without a license can get into the home network.
In order to exclude unauthorized access, for example, the home server is made to have a list of clients whose access is allowed so that collation with the list is executed each time access to the home server is requested from a client. In this way, unauthorized access can be excluded.
For example, MAC address filtering is known, which uses a MAC (Media Access Control) address corresponding to a physical address unique to each communication apparatus to set it as an access-allowable device list. More specifically, a MAC address of each device whose access is allowed is registered on a router or a gateway for isolating the internal network such as the home network and the external network from each other. A MAC address assigned to a received packet and the registered MAC address are collated with each other. Access from a device with an unregistered MAC address is refused (see, for example, Japanese Patent Application Publication No. 10-271154).
In order to construct the access-allowable device list, however, it is necessary to check the MAC addresses of all the devices connected to the internal network. Moreover, efforts to input all the acquired MAC addresses so as to create a list are required. Furthermore, in the home network, a connected device is relatively frequently changed. Therefore, the access-allowable device list has to be modified for each such change.